1. Technical Field of the Invention
The invention relates generally to the field of semiconductor devices and, more particularly, to electric fuse programming.
2. Description of Related Art
In integrated circuits including CMOS integrated circuits, it is often desirable to be able to permanently store information, or to form permanent connections of the integrated circuit after it is manufactured. Fuses or devices forming fusible links are frequently used for this purpose. For example, fuses can be programmed to replace defective elements with identical redundant elements. Further, fuses can be used to store die identification or other such information, or to adjust the speed of a circuit by adjusting the resistance of the current path.
A conventional circuit for programming a fuse is shown in FIG. 1 in which the fuse is connected between the drain of a programming transistor and a supply voltage VDD. Initially, the resistance of the fuse is small (in the range of 100 ohms). The fuse is programmed by switching ON the programming transistor with a pulse applied to the gate. When the transistor is turned ON, the transistor starts to conduct and current flows through the fuse. The current flow causes the fuse to heated-up, and if sufficient current continues to flows through it, it will get programmed by melting, electrormigration or other mechanisms, resulting in a much higher resistance (i.e., programmed resistance).
The programming transistor must have the capacity to carry the current required to program the fuse. In order to achieve that capacity, the width of the programming transistor is appropriately chosen. For poly-silicide fuses, the peak current required for programming can be of the order of 10 mA or more. This order of current requires a wide programming transistor (in the range of 40 microns for a gate oxide thickness of 6.5 nm), hence the silicon area required for implementation can be significant even if the individual fuse element itself is small.
Exacerbating the problem is the fact that most integrated chips include multiple fuses such as the multiple fuse circuit shown in FIG. 2. In DRAM chips, for example, a few thousand fuses are generally used. The large size of individual programming transistors combined with the large number of transistors can be quite costly because of the silicon wafer area consumed. Hence, there is a need for an innovative approach for programming electrical fuses which results in wafer area reduction and/or increased programming current capability.
The present invention achieves technical advantages as an apparatus, system and method of programming an electrical fuse using a transistor with active well bias. With the programming transistor operated with an active well bias, more energy is enabled for programming the fuse than is available without biasing the well for the same size transistor. Thus, a smaller transistor can be used for programming the fuse. In a multiple fuse embodiment, the programming transistors can be arranged in the same xe2x80x9cwellxe2x80x9d with a common independent Vbias applied, via a body control circuit, to the entire well during programming of a select fuse.